Atlantic tropical disturbance 91L poses little threat

By: Dr. Jeff Masters , 2:15 PM GMT on April 21, 2011

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A tropical disturbance (91L) near 24N, 63W, midway between the Virgin Islands and Bermuda, is moving north-northwest at about 8 mph. The system's heavy thunderstorm activity has increased since yesterday, but 91L has an elongated and poorly-organized circulation, thanks to a hefty 80 knots of wind shear. The storm is over waters of 25°C, and these waters will cool to 24°C by Friday as the storm continues to the north-northwest. Before 91L reaches Bermuda, steering currents will reverse and force 91L to the south-southwest on Saturday, into a region of higher wind shear. The latest SHIPS model forecast predicts wind shear will drop to 50 knots over 91L by Friday, then increase again to 70 knots by Sunday. The high shear and relatively cool water temperatures will make it difficult for 91L to organize into a subtropical depression. I give 91L a 10% of becoming a subtropical depression. Climatology argues against 91L becoming the first named storm of the year; there has only been once named April storm in the Atlantic since 1851, Tropical Storm Ana of 2003. The formation of a tropical disturbance at this location this time of year is unusual, but is not necessarily a harbinger of a active season ahead.


Figure 1. Morning satellite image of the Atlantic tropical disturbance 91L.

Jeff Masters

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Quoting alfabob:
I think 91L is nearing the end of it's northward motion, also some new convection going off at the LLC. Look's like there is a band pulling in warming moisture from the south also; this should be named at some point.


For a 10% Invest, it's very impressive.
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Personally I'm beginning to think this year might be close to 2005, i know an early start has no bearing on what a season might bring or vice versa , but 91L is impressive for April.
I think we might get a named system before June 1 anyway, 91L or not. Everyone Have a happy and safe Easter

Member Since: April 29, 2007 Posts: 0 Comments: 8134
Quoting Xyrus2000:


The models themselves are not large, and how long it takes to run them depends upon the resolution you run them at. A course resolution weather model can easily run on most desktops in a reasonable amount of time. Getting a model to compile and run a test case usually isn't the hard part as long as you're sticking with a roughly equivalent linux flavor and libraries. The hard part is setting up the model to do something useful. This usually includes figuring out what parameters to set, what data is needed, gathering said data, and setting output products. Then after that, there is the post processing which can be another programming effort entirely.

Models are and have been written by scientists for scientists, not for the general user. This is an important distinction when compared to modern software usability and design. The scientists who write models are usually not software engineers, and it shows. The worst code I have ever seen is inside scientific models. Scientific code contains a veritable cornucopia of how to NOT write good software.

Getting back to visualization software, there's a couple others out there that aren't as heavy-weight as IDV. Panoply is java app that can read and display netcdf files. There's also ncview though it is a little less user friendly. There's also HDFView if the data is in HDF format. And if you like command lines and want to get "old skool" there is Grads, which can read just about anything (but the graphics come out of the '90's).

There's also some more powerful (but programmatic) ways to view data, such as python's matplotlib and basemaps (a quasi-replacement for MATLAB).


But scientists are expected or required to be super computer savvy. Don't get me wrong, as someone going to school to be a scientist, much of what I do involves computers, but not all of of us are Linux lovers. I really could care less about computer programming and getting into the deeper computer skills. I'm very thankful for it, and all power to those who love computer science, but it bores me to death. I would do whatever I could to avoid using Linux.

Degrees in meteorology don't require any classes in computer programming or deeper computer skills. I mean, there are grad programs for guys who want to do computer model programming, but its not required as a need, thankfully! I'll take theoretical calculus and differential equations over computer programming any day!
Member Since: August 21, 2008 Posts: 0 Comments: 7992
Complete Update





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From April 1-10, 2011, the ITF remained fairly below-average in the both in position and intensity across portions of the Gulf of Guinea region, and the semi-arid parts of the lower Sahel. The mean western portion of the ITF was approximated at 10 degrees north, which lagged behind the climatological mean by more than one 1 degree for early April. The below average position was associated with rains and mositure confined along coastal Ghana and the Lake Volta area. The mean eastern portion of the ITF was approximated at 8.3 degrees north, and fell slightly behind the climatological mean for early April. The near-neutral position was associated with marked dryness in southern Sudan, and locally high rainfall in northern parts of the Central African Republic. The above map (Figure 1) shows the current ITF position relative to the positions of climatology for the first dekad of April. Figures 2 and 3 are time series illustrating the latitudinal means of the western and eastern portions of the ITF, respectively, and the start of their progress compared to climatology from the beginning of April, 2011.

Link
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Quoting Levi32:
SSTs drop off rapidly from here the farther north 91L drifts.



But it will begin to drift back to the Southwest pretty soon, at least the models say so, the question is, how far north will it go into cooler water before it turns back to the west and southwest? Also, how quickly will it begin to encounter the much higher shear?

What is kinda boggling me about this system. Is I have seen both entirely tropical and subtropical cyclones appear to be so much more unorganized this one be officially listed as named systems. To be honest, it looks pretty decent to me when you compare it to some other 40 mph tropical storms or sub-tropical storms that have come before it...


I guess they have other reasons as professionals for classifying something or not classifying it. They have access to models and computers that probably break down the low pressure into a math/physics viewpoint, telling them things about a system that you can't see.

The eye can be deceiving, but math and physics never lie. And for those who may not realize the technical about weather science. There's way more advanced math and intense physics involved in weather than you could ever imagine, believe me, this is coming from someone working my butt off for a MET degree. That's why its so dang hard to predict. Very complicated math, this giant machine we call weather is extremely complicated. That's part of why I love about it, weather in a way, is a bit of a final frontier.
Member Since: August 21, 2008 Posts: 0 Comments: 7992
Andover Kansas tornado. The video quality is poor, but the best footage is about 3 and a half minutes into the movie. April 26 will mark the 20th anniversary for this deadly twister that just missed over 80 aircraft at McConnell Air Force Base. Including two B-1 bombers fully armed with nuclear weapons and on alert the time the storm hit..P.S...This was an f-5....Link
Member Since: September 27, 2007 Posts: 1 Comments: 22307
Quoting flsky:


Incredible pic. I think it goes against human nature not to seek some kind of shelter in these situations. It's important to get the word out that this can be VERY dangerous b/c the configuration of the overpass becomes like a sluice. Wind pressure is concentrated and stronger. Lying in a ditch seems counter-intuitive, but the physics bears it out.


Sometimes we need to trust our instincts, and other times we need to trust scientific understanding.

Often though, people either lack too much of one or the other. For example, some lack too much in scientific understanding saying its needless and trust meaningless rumors or their "gut" when their feeling is wrong because sadly they just don't have any knowledge about the issue to make an accurate judgment.

While other times some people only have scientific understanding and reject the natural human ability to make accurate judgment calls on something that can't be proven or known for sure.


Balance is key :)

Member Since: August 21, 2008 Posts: 0 Comments: 7992
SSTs drop off rapidly from here the farther north 91L drifts.

Member Since: November 24, 2005 Posts: 635 Comments: 26698
Quoting Levi32:


Whatever criteria they pick, I would probably be fine with, as long as they were consistent.
Thanks, and yea definitely agree with the last part
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Quoting TomTaylor:
Levi, lets say you worked at the NHC and were lead meteorologist. Would you give 91L a name? or no


If we had the same written definition of a subtropical cyclone that we do now, and we were supposed to go by that definition, then yes I would. However, I am also perfectly fine with modifying that definition, since the practice of naming subtropical systems is still not that old and solidified yet.

The only thing I would like to see is the NHC picking clear criteria and then following them every time, instead of making decisions so confusing. Whatever criteria they pick, I would probably be fine with, as long as they were consistent.
Member Since: November 24, 2005 Posts: 635 Comments: 26698
326. flsky
Quoting beell:
Seeking shelter from a tornado underneath an overpass is still considered an extremely bad idea also. Lower is always better. Hiding under an overpass puts you 10-20' up in the stronger above-ground tornadic winds. An overpass can also serve to focus/increase the winds. A Venturi Effect.

The photo below is from the May 3rd, 1999 Oklahoma Tornado Outbreak. This is the 16th St. bridge crossing I-44 near Newcastle, OK.

The lighter colored cement areas under this overpass are actually silhouettes left behind from individuals crouching under the bridge as the tornado scoured/splattered this area with mud, dirt and debris. There was one fatality here.

Photobucket
Image Credit: Norman, OK NWS


Incredible pic. I think it goes against human nature not to seek some kind of shelter in these situations. It's important to get the word out that this can be VERY dangerous b/c the configuration of the overpass becomes like a sluice. Wind pressure is concentrated and stronger. Lying in a ditch seems counter-intuitive, but the physics bears it out.
Member Since: October 24, 2006 Posts: 0 Comments: 2102
XX/INV/91L
MARK
25.98N/63.93W
Member Since: July 15, 2006 Posts: 176 Comments: 55653
RAMMB AL912011 - INVEST

Model Data
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Quoting Levi32:


I would imagine that task would be too large for a personal computer. I'm only a novice linux user myself (something I need to remedy). That screenshot is from the Integrated Data Viewer from UCAR Unidata. It's a great data visualization program. In fact Unidata has a whole lot of data processing tools available for playing with, though I don't know how to properly use them all. Computer programming is something I'm still catching up on.


The models themselves are not large, and how long it takes to run them depends upon the resolution you run them at. A course resolution weather model can easily run on most desktops in a reasonable amount of time. Getting a model to compile and run a test case usually isn't the hard part as long as you're sticking with a roughly equivalent linux flavor and libraries. The hard part is setting up the model to do something useful. This usually includes figuring out what parameters to set, what data is needed, gathering said data, and setting output products. Then after that, there is the post processing which can be another programming effort entirely.

Models are and have been written by scientists for scientists, not for the general user. This is an important distinction when compared to modern software usability and design. The scientists who write models are usually not software engineers, and it shows. The worst code I have ever seen is inside scientific models. Scientific code contains a veritable cornucopia of how to NOT write good software.

Getting back to visualization software, there's a couple others out there that aren't as heavy-weight as IDV. Panoply is java app that can read and display netcdf files. There's also ncview though it is a little less user friendly. There's also HDFView if the data is in HDF format. And if you like command lines and want to get "old skool" there is Grads, which can read just about anything (but the graphics come out of the '90's).

There's also some more powerful (but programmatic) ways to view data, such as python's matplotlib and basemaps (a quasi-replacement for MATLAB).
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Quoting flsky:


Adding some deep thought to that can be quite interesting.


Agreed, which is why I do so when necessary.
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320. flsky
Quoting KEEPEROFTHEGATE:

I worked this disaster - it was a real mess. Felt so bad for folks.
Member Since: October 24, 2006 Posts: 0 Comments: 2102
Quoting sammywammybamy:


The underlying purpose of the question was to ask about the setup of the A/B High this year.

Some years it sends Tropical cyclones into the gulf and florida (2004,2005)

Some years it sends Tropical cyclones out to sea (2010)

How does this year look compared to the past few?



Ohhh ok, sorry, I missed the point of your question. Honestly I'm too busy with college to go into the record books and assess high pressure positions of previous years and compare them to this year. Its more important that I commit my time to school so that I can become a real meteorologist :)

I'm sure someone else here may be willing to go through that trouble though?
Member Since: August 21, 2008 Posts: 0 Comments: 7992
318. flsky
Quoting KoritheMan:


Harshness and audacity is the name of my game.


Adding some deep thought to that can be quite interesting.
Member Since: October 24, 2006 Posts: 0 Comments: 2102
Quoting Levi32:


The subtropical jet is up at around the 200mb level. It is supplying cyclonic vorticity to the upper low west of 91L, but since the winds are in the upper atmosphere, they don't aid in low-level cyclonic vorticity.
Levi, lets say you worked at the NHC and were lead meteorologist. Would you give 91L a name? or no
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Quoting sammywammybamy:
hahahahaha that's harsh.... Lmao


Harshness and audacity is the name of my game.
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Member Since: July 15, 2006 Posts: 176 Comments: 55653
Quoting WeatherNerdPR:
Interesting. I'm gone for a few days, and we get an Invest in April.

I thought it was because Dr. Masters was supposed to be going on vacation.
Meanwhile, back at the ranch, there is some rain in Texas!
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Quoting KEEPEROFTHEGATE:
don't be a dufus rufus


Keeper- you rock my world!!! hahahahaha
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Quoting KEEPEROFTHEGATE:
don't be a dufus rufus


Don't worry. Anytime Rufus says something, he has absolutely nothing to back it up.
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308. DDR
Interesting.
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Quoting RufusBaker:
looks like wind shear will be dominating the atlantic this season
don't be a dufus rufus
Member Since: July 15, 2006 Posts: 176 Comments: 55653
Ozone Hole Linked to Climate Change All the Way to the Equator



The ozone hole above Antarctica as of Oct. 12, 2006. The ozone hole has affected the entire circulation of the Southern Hemisphere all the way to the equator. (Credit: NOAA)

ScienceDaily (Apr. 21, 2011)- In a study to be published in the April 21st issue of Science, researchers at Columbia University's School of Engineering and Applied Science report their findings that the ozone hole, which is located over the South Pole, has affected the entire circulation of the Southern Hemisphere all the way to the equator. While previous work has shown that the ozone hole is changing the atmospheric flow in the high latitudes, the new Columbia Engineering paper demonstrates that the ozone hole is able to influence the tropical circulation and increase rainfall at low latitudes in the Southern Hemisphere.

This is the first time that ozone depletion, an upper atmospheric phenomenon confined to the polar regions, has been linked to climate change from the Pole to the equator.

"We show in this study that it has large and far-reaching impacts. The ozone hole is a big player in the climate system!"

"It's really amazing that the ozone hole, located so high up in the atmosphere over Antarctica, can have an impact all the way to the tropics and affect rainfall there -- it's just like a domino effect," said Sarah Kang, Postdoctoral Research Scientist in Columbia Engineering's Department of Applied Physics and Applied Mathematics and lead author of the paper.

Link
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Member Since: July 15, 2006 Posts: 176 Comments: 55653
Quoting RufusBaker:
looks like wind shear will be dominating the atlantic this season




wind shear caster
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Interesting. I'm gone for a few days, and we get an Invest in April.
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looks like wind shear will be dominating the atlantic this season
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Melting Ice on Arctic Islands a Major Player in Sea Level Rise


This ice channel, or supraglacial melt channel, was formed by meltwater flowing along the surface of the Belcher Glacier on Devon Island in Nunavut, Canada. It was photographed in August 2009. (Credit: Angus Duncan)

ScienceDaily (Apr. 21, 2011)- Melting glaciers and ice caps on Canadian Arctic islands play a much greater role in sea level rise than scientists previously thought, according to a new study led by a University of Michigan researcher.

The 550,000-square-mile Canadian Arctic Archipelago contains some 30,000 islands. Between 2004 and 2009, the region lost the equivalent of three-quarters of the water in Lake Erie, the study found. Warmer-than-usual temperatures in those years caused a rapid increase in the melting of glacier ice and snow, said Alex Gardner, a research fellow in the Department of Atmospheric, Oceanic and Space Sciences who led the project. The study is published online in Nature on April 20.

"This is a region that we previously didn't think was contributing much to sea level rise," Gardner said. "Now we realize that outside of Antarctica and Greenland, it was the largest contributor for the years 2007 through 2009. This area is highly sensitive and if temperatures continue to increase, we will see much more melting."

Link

American Pikas: Contemporary Climate Change Alters the Pace and Drivers of Extinction

ScienceDaily (Apr. 20, 2011) %u2014 Local extinction rates of American pikas have increased nearly five-fold in the last 10 years, and the rate at which the climate-sensitive species is moving up mountain slopes has increased 11-fold since the 20th century, according to a study soon to be published in Global Change Biology.

Link
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The upper low is now about 50 to 150 Miles west of the LLC, by midnight it should get on top.
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Quoting HurricaneDean07:
Levi, Question for you... Do you think due to 91L lifting North of the Sub-tropical jet, the Westerlies would help give that spin to help it re-close the LLC


The subtropical jet is up at around the 200mb level. It is supplying cyclonic vorticity to the upper low west of 91L, but since the winds are in the upper atmosphere, they don't aid in low-level cyclonic vorticity.
Member Since: November 24, 2005 Posts: 635 Comments: 26698
http://www.youtube.com/watch?v=NB1qzOhSPhI&feature= player_embedded
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Levi, Question for you... Do you think due to 91L lifting North of the Sub-tropical jet, the Westerlies would help give that spin to help it re-close the LLC
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Member Since: September 10, 2007 Posts: 0 Comments: 11518
Quoting sammywammybamy:




IMO, this looks like a Subtropical depression.

1009 mb is worthy of tropical depression status.
35Kts = 40.3mph
LLC = Present
Water temps = high enough
Satelite = Ok

They could classify it if they wanted too.

No matter how organized this thing gets it will get ripped to shreads when it gets shoved south back into the shear.


It's possible they're looking for some more curvature within the bands. Yes, a subtropical cyclone by definition has its strongest winds, and thus convection, well-removed from the center. But satellite imagery does not indicate much in the way of cyclonic banding at this time.
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Quoting sammywammybamy:


But you see it cannot recurve though...

The Ridge is pushing it into the Bahamas...

It might even get sent into Cuba as the AVNO depicts. (Although that is unlikely)


You are right, so it is actually not your stereotypical quasi-tropical system. Looking at some weather charts it looks like it might disintegrate into an open trough by the time it is near the Bahamas, has this possibility been shown in the models?
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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